Field of the Invention
The present invention relates to medical caps used for chemical bottles, infusion container bottles, and the like.
Description of the Prior Art
Conventionally, there have been caps for chemical bottles or infusion bottles used for intravenous drips in medical fields, such as a rubber plug cap, and a cap comprising a plug with a substantially columnar shape for needle sticking made of a rubber or a thermoplastic elastomer resin and an outer frame that holds said plug for needle sticking since it is required to take out the medical solutions and the like by needles. For medical caps used for these infusion bottles and the like, a sealing property is required when attached to bottles from the view point of preventing leakage of the medical solutions. Here, the plug made of a rubber component is used, and it is excellent in a re-sealing for repeated needle sticks, but it requires a vulcanizing process during the producing process that causes contamination of production environment, and so, it causes high production costs since it requires a post process such as cleansing and the like. In addition, general structures for the rubber component used to be that the film part made of the same or the same kind of a material is provided as that of the wetted surface part of the cap body in the wetted surface (lower bottom part) of the plug, or that resins are laminated on the plug and fused with the cap body, in order to prevent the cap from falling off at the time of needle sticks. Due to these factors, further high production cost has been caused by the caps using the rubber plugs.
On the other hand, in the case of the plugs whose components are thermoplastic elastomer resins, since they can be molded under clean environment, no cleansing process is required. In addition, a series of processes can be incorporated in a production process line of caps. Further, since a molding method enables the plug itself to be fused with a cap body, it is not always necessary to provide such a structure with the above mentioned film part or conduct laminating process. Therefore, in mass production, cost performance is more advantageous than that of rubber component caps. However, since thermoplastic elastomer resins have larger residual distortion than rubbers and are inferior in rubber elasticity, there used to be the problem including slipping out of the needles when sticking them or lack of a re-sealing property for the prevention of liquid leakage after needle sticks.
As solving measures for this problem, we have proposed the medical caps with improved rubber characteristics and an excellent re-sealing property by making the structure of the medical cap so that the wetted surface of the plug and the upper part of the holding part of the bottom surface of the outer frame are fused to each other and that the side surface of said plug and the inner wall of the side circuit part of said outer frame contact each other in a non-fused state (Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-118185).
As another approach to solve the above mentioned problem, the technique that improves the physical balance such as a sealing property at a time of needle sticks, power to hold a needle, coring, a re-sealing property of holes after needle removal and the like that are required for a plug for infusion by using a thermoplastic elastomer composition whose main material is a styrene-based hydrogenated block copolymer in which the molecular weight and its distribution are within the specific range and by integrally forming the plug in a state where a sealed body comprising said thermoplastic elastomer is pressurized in the horizontal direction by the tubular cap body made of plastic is disclosed (Patent Document 2: Japanese Patent Laid-Open Publication No. 2002-143270).
Then, as stated in the Patent Document 2, to the medical caps having a structure stated in the Patent Document 1, the medical cap might be considered to be prepared with a further improved property including the re-sealing property and the like by applying pressure to the plug in the horizontal direction.
However, in the technique of the Patent Document 1, unlike the medical caps stated in the Patent Document 2, unless it is so structured that the side surface of the plug is not fused to the inner wall of the side circuit part of the outer frame, the effect that said structure has cannot be obtained. It is not easy to produce the medical cap having a structure of pressure applied in the horizontal direction of the plug, while maintaining the non-fused state between the side surface of the plug and the inner wall of the side circuit part of the outer frame. One method is considered, that is, after an inner diameter of an inner side aperture of the outer frame is made smaller than the diameter of the plug, said plug is forced into said aperture and then coupled thereto thereby applying pressure to the plug in the horizontal direction. However, since it is difficult to conduct such operations by the machine operation in the process of producing caps, mass production is not available. And even if such operations are available, they cannot be applied for producing products practically since it is considered that the plugs may get damaged, and there is high risk of generating a defective sealing property thereby lowering yield when the plugs are deformed under said operation.